content: /* ===========================================================
   * JFreeChart : a free chart library for the Java(tm) platform
   * ===========================================================
   *
   * (C) Copyright 2000-2011, by Object Refinery Limited and Contributors.
   *
   * Project Info:  http://www.jfree.org/jfreechart/index.html
   *
   * This library is free software; you can redistribute it and/or modify it
   * under the terms of the GNU Lesser General Public License as published by
   * the Free Software Foundation; either version 2.1 of the License, or
   * (at your option) any later version.
   *
   * This library is distributed in the hope that it will be useful, but
   * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
   * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
   * License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with this library; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
   * USA.
   *
   * [Oracle and Java are registered trademarks of Oracle and/or its affiliates.
   * Other names may be trademarks of their respective owners.]
   *
   * ---------------------------------
   * NormalDistributionFunction2D.java
   * ---------------------------------
   * (C)opyright 2004-2009, by Object Refinery Limited.
   *
   * Original Author:  David Gilbert (for Object Refinery Limited);
   * Contributor(s):   -;
   *
   * Changes
   * -------
   * 25-May-2004 : Version 1 (DG);
   * 21-Nov-2005 : Added getters for the mean and standard deviation (DG);
   * 12-Feb-2009 : Precompute some constants from the function - see bug
   *               2572016 (DG);
   * 28-May-2009 : Implemented equals() and hashCode(), and added serialization
   *               support (DG);
   *
   */
  
  package org.jfree.data.function;
  
  import java.io.Serializable;
  
  import org.jfree.chart.HashUtilities;
  
  /**
   * A normal distribution function.  See
   * http://en.wikipedia.org/wiki/Normal_distribution.
   */
  public class NormalDistributionFunction2D implements Function2D, Serializable {
  
      /** The mean. */
      private double mean;
  
      /** The standard deviation. */
      private double std;
  
      /** Precomputed factor for the function value. */
      private double factor;
  
      /** Precomputed denominator for the function value. */
      private double denominator;
  
      /**
       * Constructs a new normal distribution function.
       *
       * @param mean  the mean.
       * @param std  the standard deviation (> 0).
       */
      public NormalDistributionFunction2D(double mean, double std) {
          if (std <= 0) {
              throw new IllegalArgumentException("Requires 'std' > 0.");
          }
          this.mean = mean;
          this.std = std;
          // calculate constant values
          this.factor = 1 / (std * Math.sqrt(2.0 * Math.PI));
          this.denominator = 2 * std * std;
      }
  
      /**
       * Returns the mean for the function.
       *
       * @return The mean.
       */
      public double getMean() {
          return this.mean;
      }
  
      /**
       * Returns the standard deviation for the function.
       *
       * @return The standard deviation.
       */
      public double getStandardDeviation() {
          return this.std;
      }
  
      /**
       * Returns the function value.
       *
       * @param x  the x-value.
       *
       * @return The value.
       */
      @Override
      public double getValue(double x) {
          double z = x - this.mean;
          return this.factor * Math.exp(-z * z / this.denominator);
      }
  
      /**
       * Tests this function for equality with an arbitrary object.
       *
       * @param obj  the object (<code>null</code> permitted).
       *
       * @return A boolean.
       */
      @Override
      public boolean equals(Object obj) {
          if (!(obj instanceof NormalDistributionFunction2D)) {
              return false;
          }
          NormalDistributionFunction2D that = (NormalDistributionFunction2D) obj;
          if (this.mean != that.mean) {
              return false;
          }
          if (this.std != that.std) {
              return false;
          }
          return true;
      }
  
      /**
       * Returns a hash code for this instance.
       *
       * @return A hash code.
       */
      @Override
      public int hashCode() {
          int result = 29;
          result = HashUtilities.hashCode(result, this.mean);
          result = HashUtilities.hashCode(result, this.std);
          return result;
      }
  
  }
  